Comet-chasing Rosetta probe is operational after long hibernation

THE comet-chasing space probe that has been in hibernation for almost three years has woken up and sent its first signal back to Earth.

The European Space Agency (ESA) received the all-clear message "Hello World!" from its Rosetta spacecraft some 800 million kilometres away shortly after 5am AEDT.

Rosetta was put into hibernation in 2011 to conserve energy for its long journey to meet with comet 67P/Churyumov-Gerasimenko.

If all goes as planned the probe will rendezvous with the comet in the coming months and drop a lander onto its icy surface in November.

A webcast showed jubilant scientists at mission control in Darmstadt, Germany as the all-is-well signal came in.

Europe's most ambitious exploration of space, the craft was launched in 2004 on a trek of seven billion kilometresaround the inner Solar System.

Its goal is to rendezvous in August with 67P/Churyumov-Gerasimenko, and in November send down a lander to carry out experiments on the icy wanderer. Comets are clusters of ice and dust which are believed to be remnants from the very birth of our star system.

Analysing this primeval matter should unlock secrets of how the Solar System formed and possibly how life on Earth was kickstarted.

Rosetta was placed in hibernation as it was so far from the Sun that light was too dim to power its solar array.

Scientists had to wait more than eight hours before getting the precious signal, sent from a distance of more than 800 million km, to confirm that it had woken up.

"It was a fairy-tale ending to a tense chapter," ESA said in a press release.